CN113468638B - Assembly type building heat bridge analysis method based on heat-humidity coupling - Google Patents
Assembly type building heat bridge analysis method based on heat-humidity coupling Download PDFInfo
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Abstract
The invention relates to an assembly building heat bridge analysis method based on heat and humidity coupling, which mainly considers the problems of heat transfer, humidity migration and coupling effect of an assembly building outer wall connecting piece part, numerically solves a model by a finite element method through COMSOL, reasonably analyzes an assembly building heat bridge, improves accuracy and provides a solution for the problem that the energy-saving efficiency of an assembly building does not reach the standard. The invention can provide theoretical guidance for heat preservation and energy conservation measures of the heat bridge part of the fabricated building and is beneficial to improving the utilization efficiency of resources. The method is suitable for thermal bridge analysis of various fabricated buildings.
Description
Technical Field
The invention relates to the technical field of constructional engineering, in particular to an assembly type building heat bridge analysis method based on heat-moisture coupling.
Background
At present, the problems of the assembled building in the aspect of energy-saving design can be mainly attributed to the following aspects: firstly, China has gaps in the aspects of construction technical standards and technical guidance of the fabricated building, so that designers excessively refer to heat preservation technical design rules and standards of common buildings during energy-saving design, and the consequences that the energy-saving efficiency does not reach the standard and building materials are wasted are caused after the fabricated building is constructed; secondly, the fabricated building is not well treated in site construction and design, for example, the heat preservation treatment of the construction joints is improper, so that a large amount of heat bridges are generated in the building, and the energy consumption is increased.
In addition, the building envelope is exposed to indoor and outdoor hot and humid environments, and under the combined action of temperature and water vapor partial pressure gradient, indoor and outdoor moisture can migrate through the building envelope. Moisture migration between the various layers of the building envelope not only shortens the service life of the system by degrading the materials and increasing the risk of mold growth, but also has a significant impact on indoor air humidity, heat load and moisture load. Condensation of vapors in porous materials, such as insulation and structural layers of exterior shingles, also enhances overall heat transfer.
Disclosure of Invention
The invention aims to provide a heat-moisture coupling-based method for analyzing a heat bridge of an assembly type building, which is used for performing heat-moisture analysis on heat bridges of connecting nodes of different assembly type buildings under various complex environmental conditions and providing theoretical guidance for the heat preservation design of the assembly type building.
The invention is realized by the following technical scheme:
the invention relates to an assembly type building heat bridge analysis method based on heat-moisture coupling, which is characterized by comprising the following steps:
the method comprises the following steps of (1) obtaining performance parameters of the wall material, wherein the performance parameters comprise density (kg/m3), constant-pressure heat capacity (J/(kg & K)), heat conductivity coefficient (W/(m & K)), water content (kg/m3), diffusion coefficient (m2/s) and steam permeability (kg/(m & s & Pa));
(the above material parameters can be found in literature or experiments)
Step (2) inquiring local typical year meteorological parameters including monthly average temperature T ext (° c), monthly average relative humidity phi ext Monthly average wind speed u (m/s);
step (3) selecting a three-dimensional building material heat and moisture transfer model in COMSOL Multiphysics, wherein a moisture control equation and a thermal control equation are respectively
Wherein (ρ c) eff ＝ρ m c p,m +ωc p,l (equation 3)
Where xi is the wet volume (the slope of the isothermal sorption-desorption curve) (kg/m3), phi is the relative humidity (%) of air, and D w Is the liquid water diffusion coefficient (m2/s), delta P The water vapor permeability (kg/(m.s.Pa)) P sat Is saturated vapor pressure (Pa), k eff Is an equivalent thermal conductivity coefficient, L v Is the latent heat of vaporization (J/kg), ρ, of water vapor m Is the dry material density (kg/m3), c p,m Is the specific heat of the dry material (J/(kg. K)), omega is the moisture content (kg/m3), c p,l The specific heat (J/(kg. K)) of liquid water, T the wall temperature (K), T the time(s),
is a gradient operator;
step (4), importing a three-dimensional physical model;
inputting parameters including meteorological parameters and material parameters;
selecting proper initial conditions and boundary conditions for each area according to the known conditions, wherein the boundary conditions comprise thermal boundary conditions and wet boundary conditions, and a user can select temperature, heat flux, thermal insulation, humidity, water vapor flux and moisture-proof layer boundary conditions according to the known conditions;
step (7) grid division is carried out, the COMSOL has a predefined free tetrahedral grid unit division mode in the aspect of grid division, a user only needs to select reasonable grid sizes (extreme coarsening, special coarsening, normal, refinement, special refinement and extreme refinement) to carry out grid division on a research object, the denser the grid sizes are, the more accurate the calculation is, but the longer the required calculation time is, and a solution mode and a time step length are set;
calculating a result;
and (9) selecting a plurality of different assembly type building connection modes and materials, and respectively calculating the wall temperature and the relative humidity parameter of each month according to the meteorological parameters of each month.
Further, the meteorological parameters include at least one of wind speed, temperature, humidity, solar irradiance, effective sky temperature, rainfall and salt spray concentration.
Further, the mesh size includes mesh partitioning of the study object at least for one of the following extreme coarsening, special coarsening, normal, refinement, special refinement, and extreme refinement.
Further, the wall material can be imported from a MatWeb material library.
Further, the three-dimensional physical model may be imported by SolidWorks or CAD.
The invention has the beneficial effects that: under various complex environmental conditions, different prefabricated building connecting node heat bridges are subjected to heat and humidity analysis, theoretical guidance is provided for heat preservation and energy saving measures of the prefabricated building heat bridge parts, and resource utilization efficiency is improved.
Drawings
Figure 1 thermophysical properties of the fabricated exterior sheathing structural assembly and the steel joint,
FIG. 2 is a 3D model of an assembled peripheral envelope structure;
FIG. 3 illustrates boundary conditions of an assembled enclosure structure;
FIG. 4 assembled perimeter shield structure meshing;
FIG. 5 solver setup;
FIG. 6 temperature distribution [ ° C ] of the thermal bridge cross-section of the connection;
FIG. 7 heat flux distribution [ W/m2] of the thermal bridge cross-section of the connection;
fig. 8 relative humidity distribution [% ] of the connector thermal bridge cross-section;
FIG. 9 water vapor flux distribution [ kg/(m 2. s) ] of the connector thermal bridge section;
FIG. 10 is a three-view and 3D model of an assembly building connector thermal bridge;
FIG. 11COMSOL solving flow chart.
Detailed Description
The following structural drawings explain embodiments of the present invention in detail. The invention can be implemented in many different ways, which are defined and covered by the claims.
Referring to fig. 11, a method for analyzing a thermal bridge of an assembly building based on thermal-wet coupling includes the following steps:
the construction method takes a bolt connection assembly type building envelope structure in Nanchang area as an example, a certain wall body is aerated concrete, a heat insulation layer is XPS (extruded polystyrene heat insulation board), wall plastering material is cement mortar, and a floor slab is reinforced concrete.
And acquiring the performance parameters of the wall material.
TABLE 1 thermophysical properties of assembled exterior sheathing structural components and steel joints
Note that: f (x) represents the parameter as a function of the parameter x, as shown in FIG. 1.
Taking february in Nanchang as an example:
average temperature per month T ext At 6.8 deg.C and a monthly average relative humidity phi ext 81.5 percent, the average wind speed per month is 2.4m/s, and the indoor design temperature T is taken int At 21 ℃ and a relative humidity phi int The content was 60%.
Selecting a three-dimensional building material heat and moisture transfer model in COMSOL Multiphysics, wherein the moisture control equation and the thermal control equation are respectively
Wherein (ρ c) eff ＝ρ m c p,m +ωc p,l (equation 3)
Where xi is the wet volume (the slope of the isothermal sorption-desorption curve) (kg/m3), phi is the relative humidity (%) of air, and D w Is the liquid water diffusion coefficient (m2/s), delta P The water vapor permeability (kg/(m.s.Pa)) P sat Is the saturated vapor pressure (Pa). k is a radical of eff Is equivalent thermal conductivity, L v Is the latent heat of vaporization (J/kg), ρ, of water vapor m Is the dry material density (kg/m3), c p,m Is the specific heat of the dry material (J/(kg. K)), omega is the moisture content (kg/m3), c p,l The specific heat (J/(kg. K)) of liquid water.
The attachment thermal bridge site is modeled using SketchUp or other 3D modeling software and COMSOL is introduced as shown in fig. 2.
Materials are selected for the respective regions according to design conditions and initial conditions are defined, as shown in fig. 3.
Wherein the boundary condition of the outer surface is
Boundary condition of the inner surface is
The initial conditions for all panel materials were set at 60% relative humidity and 21 c (294.15K).
An unstructured non-uniform tetrahedral mesh was generated using a COMSOL automatic mesh generator, selecting the mesh size as a refinement, as shown in fig. 4. To achieve an accurate and grid independent simulation, the pores (about 10 mm) are distributed in the areas near the steel connections where the potential for variation in heat and moisture transfer is high. The large grid (about 80 mm) is distributed in non-critical areas to keep the total grid number within reasonable limits.
The monthly average temperature and humidity was used in this simulation case, so a steady state solver based on Finite Element Method (FEM) was chosen to numerically solve the coupled control equations (equations 1 and 2). The steady state Partial Differential Equation (PDE) is iteratively solved using a fully coupled approach, as shown in fig. 5. And calculating after the setting is finished.
The temperature, heat flux, relative humidity, water vapor flux, etc. in the model were extracted from the COMSOL results scheme after the calculation was completed, as shown in fig. 6, fig. 7, fig. 8, and fig. 9, respectively.
And similarly, the heat and humidity performance of the assembly type building heat bridge in other months or other connection modes can be calculated, and heat and humidity analysis can be carried out on the heat bridge of the connection node of different assembly type buildings.
Claims (5)
1. A method for analyzing a thermal bridge of an assembly type building based on heat-moisture coupling is characterized by comprising the following steps:
step (1) obtaining performance parameters of the wall material, including density (kg/m) 3 ) Constant heat capacity (J/(kg. K)), thermal conductivity (W/(m. K)), water content (kg/m) 3 ) Diffusion coefficient (m) 2 (s), vapor permeability (kg/(m · s · Pa));
step (2) inquiring local typical year meteorological parameters including monthly average temperature T ext (° c), monthly average relative humidity
A monthly mean wind speed u (m/s);
step (3) selecting a three-dimensional building material heat and moisture transfer model in COMSOL Multiphysics, wherein a moisture control equation and a thermal control equation are respectively
Wherein (ρ c) eff ＝ρmc p,m +ωc p,l (equation 3)
Xi is the wet volume (kg/m) 3 ) Phi is the relative humidity (%) of the air, D w Is a liquid water diffusion coefficient (m) 2 /s)，δ P The water vapor permeability (kg/(m.s.Pa)) P sat Is saturated vapor pressure (Pa), k eff Is an equivalent thermal conductivity coefficient, L v Is the latent heat of vaporization (J/kg), ρ, of water vapor m Is dry material density (kg/m) 3 )，c p,m The specific heat (J/(kg. K)) of the dry material, and ω is the moisture content (kg/m) 3 )，c p,l The specific heat (J/(kg. K)) of liquid water, T the wall temperature (K), T the time(s),
is a gradient operator;
step (4), importing a three-dimensional physical model;
inputting parameters including meteorological parameters and material parameters;
selecting proper initial conditions and boundary conditions for each area according to the known conditions, wherein the boundary conditions comprise thermal boundary conditions and wet boundary conditions, and a user can select temperature, heat flux, thermal insulation, humidity, water vapor flux and moisture-proof layer boundary conditions according to the known conditions;
step (7) grid division is carried out, the COMSOL has a predefined free tetrahedral grid unit division mode in the aspect of grid division, a user only needs to select reasonable grid size to carry out grid division on a research object, the denser the grid size is, the more accurate the calculation is, but the longer the required calculation time is, and a solution mode and a time step length are set according to requirements;
calculating a result;
and (9) selecting a plurality of different assembly type building connection modes and materials, and respectively calculating the wall temperature and the relative humidity parameter of each month according to the meteorological parameters of each month.
2. The assembly building thermal bridge analysis method based on thermal-wet coupling as claimed in claim 1, wherein:
the meteorological parameters include at least one of wind speed, temperature, humidity, solar irradiance, sky effective temperature, rainfall and salt spray concentration.
3. The assembly building thermal bridge analysis method based on thermal-wet coupling as claimed in claim 1, wherein:
the grid size comprises at least grid division on a research object in one of the following extreme coarsening, special coarsening, normal, thinning, finer, special thinning and extreme thinning.
4. The assembly building thermal bridge analysis method based on thermal-wet coupling as claimed in claim 1, wherein:
the wall material can be imported from a MatWeb material library.
5. The assembly building thermal bridge analysis method based on thermal-wet coupling as claimed in claim 1, wherein:
the three-dimensional physical model may be imported by SolidWorks or CAD.
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| CN108009309A (en) * | 2017-10-17 | 2018-05-08 | 西安建筑科技大学 | A kind of construction material thermal conductivity factor computational methods |
| CN111812147A (en) * | 2020-06-24 | 2020-10-23 | 浙江大学 | Design method of soil heat-moisture coupling transfer modeling experiment containing heat source |
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| CN108009309A (en) * | 2017-10-17 | 2018-05-08 | 西安建筑科技大学 | A kind of construction material thermal conductivity factor computational methods |
| CN111812147A (en) * | 2020-06-24 | 2020-10-23 | 浙江大学 | Design method of soil heat-moisture coupling transfer modeling experiment containing heat source |
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